1. Field of the Invention
The present invention relates to an electrochemical apparatus which detects a gas concentration by using a solid-electrolyte and a method of manufacturing the above electrochemical apparatus, and more particularly relates to an electrochemical apparatus which has small variation in output signals therebetween with respect to the same gas to be measured.
2. Related Art Statement
Heretofore, as an apparatus comprising an electrochemical cell using the solid-electrolyte such as an oxygen sensor which detects an oxygen concentration in an exhaust gas from an internal combustion engine, there has been known a sensor wherein an electrochemical cell is constructed from a zirconia porcelain as the solid-electrolyte having an oxygen ion-conductivity and a pair of porous electrodes, and an electrochemical pumping is effected by flowing a current through a pair of porous electrodes, while one of the porous electrodes is brought into contact with an outer gas to be measured through a gap having a gas diffusion resistance or a diffusion means such as porous ceramics etc., and a pumping current corresponding to the outer oxygen concentration is outputted. Further, there has been known a detector (electrochemical apparatus) for detecting a hydrogen gas, a carbonic acid gas, etc., by utilizing an electrochemical pumping and a gas diffusion theory, as is the same as the oxygen sensor mentioned above.
However, when large scale manufacturing is performed for the known electrochemical apparatus, there is a drawback that diffusion resistances of the diffusion means in the electrochemical cells are largely varied, respectively, so that the outputs of respective apparatus are not constant with respect to the same gas to be measured, i.e. it is difficult to obtain the electrochemical apparatus. With constant quality.
Further, as for the diffusion means having a diffusion resistance with respect to a gas to be measured, use is made of a plain gap or a pin-hole brought into contact with the outer gas to be measured and surrounded by a ceramic body such as the solid-electrolyte, or a porous ceramic layer formed by a flame spraying, or a burning after screen printing or laminating. In this case, since the diffusion resistances between respective electrochemical cells largely vary corresponding to the conditions such as a dimension of the solid-electrolyte ceramic body, a thickness of the gap in laminating, amounts of warp and a deformation in burning and the flame spraying condition, it is also difficult to obtain the electrochemical apparatus with constant quality.